It's an age-old question: What makes a woman dress to impress?
A new report says the answer might be in the ovaries.
According to a study done by UCLA and the University of Wisconsin-Eau Claire, women put more time and effort into their appearance when they're ovulating.
Clothes and makeup aren't the only things that change at that time of the month: Women's strength, appetite and attitudes toward men and each other change as well.
The study's lead author, UCLA professor Martie Haselton, explained how she and her researchers had come to the conclusion that ovulation affects a woman's appearance.
"What we did was photograph the women on a high fertility day and a low fertility day, and we showed those photographs to a separate set of judges, and we asked them, 'In which photo is the woman trying to be more attractive?'" she said.
The judges picked a woman's high fertility photograph 60 percent of the time -- a rate much higher than random chance.
"For the women who were actually ovulating on the day of their period, it was more than 80 percent for those photos," Haselton said.
People have long thought that women hid all signs of ovulation, even from themselves and their mates. Haselton's study shows that many signs do exist, though they're subtle.
"Women experience a decrease in appetite near ovulation, even though there's an increased caloric need. And that's not just compared to when they are PMSing," Haselton said.
There's also evidence that women are stronger when they're most fertile.
"There's one study that showed that women's hand strength increased during ovulation," Haselton said.
Women may even be more tempted to cheat when they're ovulating than at other times of the month. Their preferences for types of men can also change.
"They look more for facial masculinity and male scents -- the body scents that may be associated with greater testosterone," Haselton said. "They tend to go for the softer side, kind and caring, having sweet faces."
Women's interactions with each other can change too.
"There is preliminary evidence that women rate other women as less attractive during ovulation. One possibility is that they feel better about themselves. Maybe they feel better so they dress better," Haselton said.